Method and system for phase-sensitive magnetic resonance imaging

Abstract

In a method and system for phase-sensitive magnetic resonance imaging, a respective, complex image data set provided to a processor for each of at least two different echo times, the complex image data sets for the different echo times having been reconstructed from magnetic resonance data that acquired for the different echo times using an echo imaging sequence, at least one complex division image data set is determined in the processor by complex division of the complex image data sets for the two different echo times. The two different echo times define an echo time difference, so the resulting complex division image data set has phase components that are dependent on the echo time difference.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention concerns a method for phase-sensitive magnetic resonance imaging in which magnetic resonance data are acquired using an echo imaging sequence, as well as a magnetic resonance system for implementing such a method.[0003]2. Description of the Prior Art[0004]Magnetic resonance tomography (MRT) is an imaging modality that enables the acquisition of two-dimensional or three-dimensional image data sets that can depict structures inside an examination subject (even soft tissue) with high resolution. In MRT, protons in the examination subject are aligned in a basic magnetic field (B0) so that a macroscopic magnetization (alignment) of the protons exists, and the protons are subsequently excited by the radiation of RF (radio-frequency) pulses. The decay of the excited magnetization is subsequently detected by means of one or more induction coils, and a spatial coding of the acquired signal is achieved by th...

AI Technical Summary

Benefits of technology

Enables the combination of MR data from various echo times and coils with improved signal-to-noise ratio and precise determination of phase and T2* relaxation times, reducing artifacts and movement artifacts, and facilitating accelerated acquisition techniques.

Problems solved by technology

Furthermore, a combination of the magnitude data that were acquired with different coils is not optimal with regard to the signal-to-noise ratio (SNR).

However, this approach is very time-consuming and correspondingly prone to movement artifacts.

In addition to these phase shifts with information content, there is a series of effects that cause unwanted phase shifts that can conceal usable information.

These effects include, among other things, an inhomogeneity of the static B0 field, the susceptibility of articles and materials in proximity to the patient, phase shifts of the radiated RF pulses, and errors in the chronology of the acquisition sequence.

These phase shifts make it difficult to compare and combine image data acquired at different echo times with one another.

In particular, the combination of MR data acquired with different reception coils while acquiring phase information turns out to be difficult since each acquisition channel has a different phase shift.

Objects within the examination subject—for example air bubbles, implants, needles or the like—can also lead to susceptibility artifacts, and thus also to phase shifts.

Image points with large phase variation—for example in regions with low SNR or along tissue boundaries—can interfere with the phase correction method.

However, in such sequences, different spatial frequencies (k-space lines) are scanned using different TEs, such that these respectively contribute to an error in the reconstructed image data depending on the respective TE.

The errors in the phase accordingly depend on the acquisition sequence and moreover have a spatial dependency, such that they can only be predicted with difficulty.

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